Tree roots growing inside traditional sewer pipes are a common and expensive problem experienced by many council’s and water authorities, and are responsible for blockages and damaged sewer pipes.
The flow of warm water inside sewer pipes can cause water vapour to escape into the cold soil surrounding the pipe. The tree roots tips can detect minute differences in moisture and nutrient levels and tend to grow in the direction where these can be found. On reaching a crack or joint in the pipe, tree roots will penetrate the opening to reach the moisture inside the pipe.
If not disturbed once inside the pipes, tree roots will completely fill the pipe, expanding and exerting considerable pressure at the crack or joint where they entered the pipe as the roots continue to grow. The force exerted by the root growth will break the pipe and may result in total collapse of the pipe.
Severe root intrusion and pipes that are structurally damaged will require replacement.
Pipes Susceptible to Root Damage
Some pipe materials are more resistant to root intrusion than others. Vitrified clay pipe is easily penetrated and damaged by tree roots. Concrete pipes also allow root intrusions to a lesser extent than vitrified clay pipe.
PVC Pipes – Highly resistant to Root Intrusion
PVC pipe is more resistant to root intrusion because it has fewer joints. Because of their flexibility, the tightly fitting PVC joints are less likely to leak as a result of settlement of backfill around the pipe.
The Australian CSIRO and Iplex Piplelines conducted trials comparing the resistance of clay, concrete and PVC pipe joints to tree root penetration under accelerated conditions over 32 months. The report concluded that:
“The performance of the Fibre Reinforced Concrete (FRC) joints was poor compared with PVC but not quite as bad as Vitrified Clay (VC) Pipes. It was concluded that whilst surface roughness, porosity and design play a part, the pH of the pipe material is also a factor.
As a consequence of these accelerated root intrusion tests it was concluded that PVC elastomeric seal joints markedly outperformed FRC and VC pipe joints. ”
Tree root penetration of pipeline systems can result in seepage into pipelines, flooding of sewerage treatment plants and sewerage leakage out of pipeline systems.
PVC pipes clearly outperform other socket / spigot joint systems.
